It is widely acknowledged that changes in the sleep/wake system accompany aging. As a result, many older people complain of sleep disturbance. Age-related sleep changes are typically expressed as fragmented nocturnal sleep, multiple and prolonged awakenings in the second half of the night, and increased daytime sleepiness. Few elderly report difficulties getting to sleep, and thus, insomnia in people over 65 is generally regarded as a disorder of maintaining, rather than initiating, sleep. It has been suggested that such sleep disturbance is due in large part to age-related changes in the circadian system. Yet, there is growing evidence that homeostatic factors may play an important role, as well, in the etiology of age-related sleep disturbance. Significant questions remain, however, concerning the exact nature of age-related changes in the homeostatic control of sleep. To fully understand and treat sleep disturbance in aging, it is important to characterize in detail the contributions of both homeostatic and circadian processes. Because of the impact of 24-hour zeitgebers on behavioral expression of sleep, it is difficult to gain a clear view of the relationship between homeostatic and circadian processes under the entrained conditions of daily life. Rather, such examinations are best carried out under conditions in which potential masking effects are eliminated or carefully controlled. The aims of the proposed research are threefold. First, the extent to which homeostatic control of sleep may be altered as a function of normal aging will be determined and characterized. Second, the extent to which these hypothesized changes are related to age-related sleep disturbance will be examined. Finally, the temporal relationship between homeostatic aspects of sleep and the circadian timing system will be investigated. To accomplish these goals, a protocol particularly well-suited to the detailed examination of homeostatic sleep processes and their interaction with the circadian component will be employed. EEG and body temperature will be recorded during 72-hours in "disentrainment". A group consisting of sleep-disturbed and non-sleep-disturbed elderly, as well as a group of healthy young adults, will be studied. Subjects will be instructed to eat and sleep when inclined to do so, and there will be reduced behavioral options to sleep. Analyses will focus on group differences in traditional and computer-based quantitative EEG parameters, on hypothesized age differences in the circadian timing and duration of sleep, and on putative relationships between hypothesized changes in EEG brain activity and age- related sleep disturbance. This study will be the first to intensively examine circadian and homeostatic processes in aging and age-related sleep disturbance, as they interact within the framework of spontaneous sleep and wakefulness. It is expected that this important first study will form the basis for future investigations to develop more effective non-pharmacological treatments for alleviation of age-related sleep maintenance insomnia.